1. Field of the Invention
The present invention relates to a vibration wave driving apparatus that causes a vibration body to generate a vibration wave by applying an alternating voltage to an electro-mechanical energy conversion element to drive a moving body by the vibration wave.
2. Description of the Related Art
A vibration wave driving apparatus as described in Japanese Patent Application Laid-Open No. 2004-304887 is proposed in the past as a linear ultrasonic motor that linearly drives a driven body.
The driving principle of such a linear ultrasonic motor will be described by using FIGS. 4A to 4C. As shown in an outside perspective view of a linear ultrasonic motor in FIG. 4A, a linear ultrasonic motor 410 includes a vibrator 401, a slider 406, and a pressing member (not shown) to press the vibrator 401 against the slider 406.
The vibrator 401 includes an electro-mechanical energy conversion element 405 such as a piezoelectric element and an elastic body 402 joined to one side of the electro-mechanical energy conversion element 405 for integration and formed in a rectangular shape.
Further, the vibrator 401 includes two projecting portions 403, 404 formed in a convex shape on the upper surface of the elastic body 402.
In the ultrasonic motor, the vibration for driving is generated by exciting a plurality of desired vibration modes by applying the voltage of a specific frequency to the piezoelectric element and superposing these vibration modes.
In the motor in FIG. 4A, the vibrator 401 is caused to excite two bending vibration modes shown in FIGS. 4B and 4C.
Both of these two bending vibration modes are bending vibration modes in an out-of-plane direction of the plate-shaped vibrator 401.
One vibration mode is a secondary bending vibration mode (Mode-A) in the longitudinal direction of the vibrator 401 and the other vibration mode is a primary bending vibration mode (Mode-B) in the transverse direction of the vibrator 401.
The shape of the vibrator 401 is designed in such a way that the resonant frequencies of the two vibration modes match or are close to each other.
The projecting portions 403, 404 are arranged close to positions as nodes of vibration in the Mode-A vibration and apical surfaces 403-1, 404-1 of the projecting portions make a pendulum motion due to the Mode-A vibration with nodes of vibration acting as a fulcrum and thus make a reciprocating motion in the X direction. That is, the apical surfaces 403-1, 404-1 of the projecting portions make a reciprocating motion in a direction along which the slider serving as the driven body moves relatively due to the Mode-A vibration.
The projecting portions 403, 404 are also arranged close to positions as loops of vibration in the Mode-B vibration and the apical surfaces 403-1, 404-1 of the projecting portions make a reciprocating motion in the Z direction due to the Mode-B vibration. That is, the apical surfaces 403-1, 404-1 of the projecting portions make a reciprocating motion in a direction along which the slider serving as the driven body is knocked up (corresponding to the direction perpendicular to the apical surface of the projecting portion) due to the Mode-B vibration.
The apical surfaces 403-1, 404-1 of the projecting portions make an elliptical motion in an XZ plane by simultaneously exciting and superposing these two vibration modes (Mode-A and Mode-B) in such a way that a vibration phase difference is close to ±π/2.
The pressure-contacted slider 406 can be driven in one direction by the elliptical motion.
On the other hand, a vibration wave driving apparatus as described in Japanese Patent Application Laid-Open No. S61-224882 is proposed in the past as a rotary ultrasonic motor that rotates a driven body.
This kind of vibration wave driving apparatus is shown in FIG. 5A.
In FIG. 5A, an elastic body 502 has an annular shape and a plurality of projections 502b is provided in an upper part thereof all around the elastic body 502. A moving body 503 is in pressure-contact with the elastic body 502 by a pressing member (not shown).
The moving body 503 includes a ring-shaped body portion 503a formed of an elastic member, a flange portion 503b extending from the body portion 503a, and a contacting portion 503c extending from an end of the flange portion 503b and having a frictional surface that is frictionally in contact with the elastic body 502.
A piezoelectric element 501 is bonded to the bottom of the elastic body 502 by an adhesive and generates a traveling vibration wave by an alternating voltage having a phase difference being applied by a driving circuit (not shown) when a motor is driven. If the traveling direction of the traveling vibration wave is a direction in which the θ direction is positive (see an arrow in FIG. 5A), the direction of movement of the moving body 503 driven by friction is a direction in which the θ direction is negative.
A motor that rotates the moving body 503 described in Japanese Patent Application Laid-Open No. S61-224882 can be produced by arranging, instead of the elastic body 502 and the piezoelectric element 501 described in Japanese Patent Application Laid-Open No. S61-224882, a plurality of the vibrators 401 described in Japanese Patent Application Laid-Open No. 2004-304887 in such a way that the longitudinal direction of the vibrator 401 matches the rotational direction of the moving body.
FIG. 5B shows a case when, for example, the three vibrators 401 are arranged. If the apical surfaces 403-1, 404-1 of the projecting portions of the vibrator 401 and the contacting portion 503c of the moving body 503 are brought into pressure-contact and the vibrator 401 is caused to excite two bending vibration modes, the moving body 503 rotates.